Electrodeposition of Granular Cu-Co Alloys

Abstract

Electrodeposition characteristics of Cu-Co films were studied for the formation of heterogeneous alloys for giant magnetoresistance applications. In situ scanning tunneling microscopy, Auger electron spectroscopy ͑AES͒, and high resolution scanning electron microscopy studies showed that rough films with a low concentration of cobalt ͓Cu92.5-Co7.5͔ ͑atom %͒ were deposited mainly due to a higher deposition rate of copper than of cobalt toward the end of the deposition process, and due to the formation of copper grains after the electrodeposition process by chemical exchange between copper ions in the solution and with the cobalt in the deposit. AES analysis revealed that the Cu-Co film is not homogeneous; the bulk of the film is richer in Co while the surface and the bottom of the film are Co-poor. X-ray diffraction showed that the electrodeposition is a topotaxial crystallization process and that the as-deposited film is composed of two phases, a solid solution of face centered cubic Cu-Co with preferred orientation of ͕111͖ planes, and a hexagonal close packed Co phase. Scanning electron microscopy micrographs and energy dispersive spectroscopy indicated the segregation of cobalt grains resulting from thermal treatments, according to the phase diagram of Cu-Co.One of the most exciting and startling properties exhibited by some magnetic multilayer systems is the giant magnetoresistance ͑GMR͒ effect. GMR refers to a significant change in the electrical resistance of a film or a device when an external magnetic field is applied. The GMR effect which was first discovered in magnetic multilayers 1 also exists in heterogeneous alloys with ferromagnetic granules ͑i.e., Fe or Co͒ embedded in a nonmagnetic metal ͑i.e., Cu or Ag͒. 2 Heterogeneous alloy films are a potentially useful alternative for GMR applications, especially for magnetic sensor applications, where the sensitivity is less important than the magnitude of the response. 2 It is generally simpler to prepare a heterogeneous alloy film rather than a multilayer system. The heterogeneous alloy films are immiscible combinations usually prepared by physical deposition methods. 3,4 An alternative processing technique is electrodeposition. 5-13 Electrodeposition has several advantages over dry processes. There are a large number of possible alloy combinations. Electrodeposition does not require vacuum technology and consequently is less expensive. It can easily be scaled up for use in large size areas, and it is capable of depositing uniform films on complex surfaces without shadowing effects often encountered in other deposition methods. The experimental systems used are much simpler than evaporation or sputtering apparatus, and electrodeposition can be a roomtemperature technology. There are some drawbacks associated with the process such as the need for a conducting/semiconducting substrate, the limited number of elements that can be deposited, and the large number of variables that control this process ͑composition, pH, concentration, current density, temperatur...

A study of the electrodeposition of Co–Cu alloys thin films on FTO substrate

“…In order to obtain a Co-rich deposit at the high-cathodic potential region, the copper sulfate content in the solution was set at significantly low in comparison with the cobalt sulfate. In this system, the film composition is influenced by deposition potential, ion concentration, additives, pH, deposition temperature, and agitation of the solution [7,11,[13][14][15]. As shown in Fig.…”

“…However, the electrodeposition made the Co-Cu alloy in nonequilibrium supersaturated solid solution state. It is well known that the nucleation-growth process, the morphology, the microstructures, and magnetic properties of Co-Cu electrodeposits depend greatly on solution composition, pH, temperature, and current density or applied potential [11][12][13][14][15][16]. Several baths with different compositions have been used for electrodeposition of CoCu thin films.…”

Influence of cathodic current density and mechanical stirring on the electrodeposition of Cu-Co alloys in citrate bath

“…In citrate baths, this can be obtained mainly with citrate solution concentration higher than 0.5 mol.L -1 and low polarization values 9 . Cohen-Hyams et al 1 have shown that thin CuCo films presented a negligible concentration of cobalt atoms at the surface, which went through a peak concentration before gradually decreasing close to the substrate, while copper deposition followed the opposite direction. The authors suppose that copper grains are formed on the substrate and, as the deposition process progresses, the substrate changes to the Cu-Co mixture, either as a metastable solid solution and/or as nanoclusters of cobalt inside a matrix of copper.…”

“…Cu-Co alloys, deposited on copper, platinum or silicon substrates, have been presenting great interest due to their possible use in data store systems and sensor technology [1][2][3] . The above mentioned applications are based on the giant magneto resistance properties presented by these alloys, which promotes a great variation of electrical resistance in an external magnetic field.…”

A Cobalt Film Electrode for Nitrite Determination in Natural Water

“…The literature mentioned that pH around 4 was the best for Co electrodeposition onto metal substrate [31,35]. To maintain this pH value, boric acid was frequently used as a buffer agent [28,31,33,35,36].…”